Hybrid Membrane and Solvent Acid Gas Enrichment for Enhanced CO2 Capture

Abstract

Abstract A novel approach for simultaneous acid gas enrichment (AGE) and CO2 capture is presented. This new process combines membrane and amine technologies to achieve unprecedented levels of H2S enrichment (>85%) and efficient CO2 capture. Traditionally, acid gas enrichment (AGE) is performed with an H2S-selective amine to elevate the H2S content of an acid gas stream, with the primary objective being to allow for reliable operation of the sulfur recovery unit (SRU). SRUs convert H2S into elemental sulfur and perform better with a high acid gas H2S concentration. The higher the H2S concentration, the higher the temperature in the reaction furnace, leading to complete destruction of hydrocarbons, including aromatics, in the acid gas feed stream that would otherwise have a detrimental effect on the downstream catalyst beds. The amine-based AGE is designed to increase the H2S concentration, preferably above 55%, and up to 70%. At this concentration, the sulfur recovery unit can operate in straight-through mode, and all hydrocarbons and feed stream contaminants are destroyed in the reaction furnace leading to trouble-free catalytic bed operation. The off-gas (i.e., overhead) of the AGE absorber, is a potential source for high purity CO2 (i.e., 98.5%+ CO2-dry basis), but with a CO2 recovery lower than 70%. Our novel approach was designed to further improve both the H2S enrichment process and CO2 capture efficiencies. The new design combines a CO2-over-H2S selective membrane and H2S-selective amine. By its physical and chemical properties, the membrane rejects hydrocarbons, including aromatics, and mercaptans along with H2S in the acid gas stream to the sulfur recovery unit. The membrane permeate contains most of the acid gas CO2 and a small amount of H2S. This membrane permeate stream is sent to an H2S-selective amine to capture H2S, which leads to a high-purity CO2 overhead stream. The CO2 capture rate can exceed 95% with a lower cost than any other commercially available solution. The H2S concentration in the acid gas feed to the SRU can simultaneously exceed 85%, which ensures reliable SRU operation as well as minimizing the size of the required SRU equipment (i.e., reduced capex). An example of the novel technology potential to capture more than 95% of CO2 from the feed of an existing SRU equipped with amine tail gas treatment (TGT) is presented.